Practically everything I’ve read from the TSR days are much more interesting than anything published under WotC. So, if you play any OGL based systems (such as DCC, OSRIC, S&W, C&C, etc.), or 5e, then it’s necessary to convert older material in some fashion.
I looked at the D&D 5e conversion guide, and found that it wasn’t very helpful. Next I looked at key types of armor.
All systems start with a base AC of 10 except in Basic D&D where it is 9.
Leather gives an AC of 8 in AD&D and 7 in Basic. It is 11 in D&D 5e and 12 in DCC.
Chainmail gives an AC of 5 in AD&D and in Basic. It is 16 in D&D 5e and 15 in DCC.
Full plate gives an AC of 2 in AD&D (but 0 in Basic) and 18 in D&D 5e and DCC.
All of the other intervening armors were similarly close (or the same).
All systems modify by 1 (either + or -) for shields.
What I found was that you can set both systems equal at 10 (with Basic offset by 1) and simply go up and down by increments of one and it’s practically the same. Especially if you are using AD&D material in DCC. So, as VS would say, “No need to convert, adapt”. So, I created a simple little table that I think would work well.